This application requests funds to purchase a cesium irradiator for the irradiation shared service laboratory at the Dartmouth-Hitchcock Medical Center (DHMC). In December 1991 the medical center will open a new hospital, clinic, and medical school with 60 laboratories 2.5 miles from its current site. Over the next several years, the remainder of the medical school facilities will move to the new site. The Irradiation shared service will be housed in a suite comprised of the irradiator room, an animal holding room, and a preparatory laboratory. It will be used by 14 investigators, each of whom has a peer reviewed and funded project in which irradiation of specimens is critical to the studies. This new facility will replace the existing irradiation facility housing a General Electric Maxitron-300 X-ray machine which has been used for 19 years. Users of the new facility will come from the departments of Biochemistry, Medicine, Pharmacology and Toxicology, Microbiology, Community and Family Medicine, Surgery, and Pathology in the Dartmouth Medical School. It will continue to be administered as a shared facility of the Norris Cotton Cancer Center (NCCC) under the direction of the Radiobiology Research Program of the NCCC. The log of the current facility shows 560 irradiation sessions in 1990 by 15 investigators with NIH-funded projects. Bacteria, chemicals, leukocytes, cell cultures, rodents, and large animals are routinely irradiated. The 19 year-old X-ray machine we currently use is becoming difficult to maintain; it will not be relocated to the new DHMC, and there are significant technical advantages to a cesium irradiator, enabling it to provide more appropriate irradiations for the biomedical research projects.